Tech Talk #39 – Bolt-On Admonitions

By David Reher, Reher-Morrison Racing Engines

“Building a racing engine is like painting a car – the preparation takes far longer than the final act.”

Walking through the aisles in a supermarket can teach you more about marketing in the 21st century than a business school textbook. It’s easy to see the hot buttons that the experts have determined will trigger a purchase decision for anything from breakfast cereal to dog food: “New!” “Improved!” “Natural!” “Low Fat!” “Low Sodium!” shout the packages. It takes a skeptical consumer to recognize the hype behind the words. Yes, a tin of lard is low sodium; that’s because it’s pure fat.

Like any marketplace, motorsports also has its share of hyperbole. Racers being racers, they will pay attention to any product that purports to improve horsepower, performance or their chances of winning. In that vein, perhaps the most abused term in racing is “bolt-on.”

This is my last column of the year for National DRAGSTER, so I will repeat some advice that I’ve offered previously. If you are planning to build or extensively modify an engine during the off-season, please remember that every part has to work with every other part to produce a reliable, dependable and powerful engine. Therefore I urge you to have a healthy skepticism about “bolt-on” parts.

This is truly the Golden Age of engine building. Racers have never enjoyed a greater selection of top-quality, competition-tested parts produced by the automakers and by aftermarket manufacturers. But while this huge variety of choices is a blessing for engine builders, it can also be a curse. There are so many options now that it is very difficult for even experienced engine builders to put together a compatible combination. The choices confronting a novice or beginning racer are simply overwhelming.

When I started building race engines more than 30 years ago, we had one choice: the small-block Chevy V8. We used junkyard cylinder heads, junkyard blocks, junkyard crankshafts. They all came from General Motors, and for the most part, they were interchangeable. As long as you remembered the differences in crankshaft journal diameters between 283, 350 and 400-cubic-inch blocks, it was fairly simple to bolt together a stout small-block racing engine. The few “bolt-on” aftermarket parts we used were limited to rocker arms, intake manifolds and headers. But even then we often had to clearance the rocker arms, machine the intake manifold flanges and rework the header pipes to make everything fit after we’d machined the blocks and heads.

Now there are literally hundreds of variations on the basic small-block Chevy theme. There are Gen I, Gen II and Gen III engines, conventional cooling and reverse-flow cooling, one-piece crankshaft seals and two-piece crankshaft seals, internally balanced cranks and externally balanced cranks, flat tappets and hydraulic roller lifters – and those are just the factory parts. Add the options in high-performance and aftermarket parts, with 18-degree, 15-degree and 12-degree heads, aftermarket cast-iron and aluminum blocks, at least three different block heights, conventional and raised camshafts – well, the number of possible combinations is stratospheric.

The same situation exists for virtually every engine used in racing today. A big-block Chevy V8 can be built with conventional siamesed-port cylinder heads or spread-port heads, a factory or aftermarket block, a production or extra-tall deck height, a standard or spread oil pan – the list is endless. Ford and Mopar races face the same mind-boggling choices.

So when I see a part being promoted as a “bolt-on,” my question is: What does it bolt onto? To cite one example, you’ll find significant differences in the spark plug locations in big-block cylinder heads. If you bolt heads with a relatively low spark plug location onto a block with high-compression pistons, the domes will almost certainly smash the spark plug electrodes. Yes, the heads will physically bolt onto the block — but the engine won’t run with them.

An item as apparently simple as a pushrod guideplate can cause big problems if doesn’t fit a specific cylinder head. A “universal” guideplate may not fit a head quite right; there are differences even among conventional big-block head castings that affect the alignment between the pushrod, rocker arm and valve stem tip. When you add the variables of valve stem length, valve angle and valve centerline locations, it’s truly miraculous when everything lines up.

Some manufacturers recognize the differences between various components and take steps address them. Unfortunately, their good intentions can cause new problems. For example, a distributor with an adjustable collar would seem to solve the problems created by differences in block heights, cylinder heads and intake manifolds. But what’s really critical when installing a distributor in a Chevy small-block or big-block V8 is the alignment between the groove in the distributor shaft and the oil gallery in the block. If the groove is too high or too low, the flow of oil to the lifters and rocker arms will be cut off. The only way to make sure that this passage is open is to remove the rear gallery plug and inspect it visually. If you just drop the distributor into the block and tighten the adjustable collar, the distributor gear may not be properly aligned with the cam gear or the oil pump shaft may not be fully engaged in the distributor gear.

Building a racing engine is like painting a car – the preparation takes far longer than the final act. A competent engine builder can assemble a short block in a few hours, but it might take weeks to inspect, mock-up, check clearances and rework all of the parts to work together properly. Building an engine is not a speed contest; if you don’t have time to do it right the first time, you better have time to do it over again.

Parts that are obviously incompatible are easy to spot and relatively simple to fix. It’s the parts that are almost right that can be the most troublesome. Suppose the rocker stud bosses in your new heads aren’t tapped quite deep enough. You torque down your expensive new shaft-mounted rocker arms and get ready to race. Unfortunately, the fasteners are bottomed out in their bolt holes, the rocker stands can move around under load, and the valvetrain is going to self-destruct on the first run.

My advice is never to assume that a part is perfect until proven otherwise. Look at every piece and ask, “What could possibly be wrong?” The guys in our shop build literally hundreds of engines every year, and it seems like every day we find some new hiccup that we haven’t seen previously. Last week we had a brand-new engine on the dyno that had a water leak. The cause turned out to be a thermostat housing bolt hole that only had three threads. The bolt was bottoming out and the gasket wasn’t compressed. So now we have one more thing to check.

Every part in a racing engine is designed and built by human hands. We know that to err is human, so it’s the responsibility of the engine builder to be the final inspector. There is a saying among engineers that Nature always sides with the hidden flaw; our job as racers is to discover the hidden flaws before they become obvious problems.

My purpose in writing this column is not to knock the manufacturers who produce the parts that power our sport, or the people who package, promote and distribute them. What I am suggesting is that you regard the claims for easy, bolt-on installation with the same healthy skepticism that you would apply to sugar-coated cereal that is billed as low-sodium, low-fat, low-cholesterol health food.